Daniel Ellsberg is admired by millions, but in the 46 years since he leaked the Pentagon Papers — a noble deed that helped end the Vietnam War — he’s been nagged by the notion that his work remains incomplete.

In his new book, the dauntless whistle-blower reveals that he planned another big leak in the 1970s but was foiled by, of all things, “an act of nature.” This second cache of documents — its existence “a closely held secret, until now” — detailed the dire business of building, testing and deploying nuclear bombs. Ellsberg, 86, says he’ll “always deeply regret” that he wasn’t able to release the papers to the public; he suggests that they might have forced a reckoning with America’s vast arsenal.

Undeterred, the former defense policy analyst has written an earnest plea for a reassessment of a weapons program that he describes as “institutionalized madness.” “The Doomsday Machine: Confessions of a Nuclear War Planner” blends personal recollections and historical analysis with a set of considered proposals for reducing the threat of apocalyptic war. Many years in the making, it’s a book that arrives at an opportune moment.

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To those yearning for a preemptive attack to “decapitate” North Korean leadership, Ellsberg has some words of caution. Ostensibly designed to avert a nuclear exchange, such an offensive would probably trigger one, he says, because Pyongyang almost certainly has a “dead hand” system that, in the event of Kim Jong Un’s demise, would prompt a “full-scale launching of their ready forces.”

Though Ellsberg has his regrets, he needn’t feel like he let anyone down. In 1971, he risked everything to leak thousands of pages from the Pentagon’s in-house history of the quagmire in Vietnam. Portions of the Pentagon Papers were published in the New York Times, the Washington Post and, later, more than a dozen other newspapers. (In Steven Spielberg’s new movie “The Post,” Ellsberg is played by Welsh actor Matthew Rhys.)

All the while, Ellsberg, who lives in the East Bay, was planning to release more secret documents — a mother lode of nuclear-weapons data. Alas, he recalls, the papers were lost when his brother hid them in a suburban New York landfill, which was later battered by a hurricane: “An act of grace, my wife, Patricia, calls it, since — though it frustrated my deepest plans and caused me great anguish — it allowed me to sleep next to her, in loving embrace, for the last forty years instead of in prison.”

A portion of the information contained in those storm-tossed papers has since been unearthed by journalists and activists. But “The Doomsday Machine” is nonetheless effective, a book that challenges some big assumptions about America’s weaponry — and questions the shaky intellectual foundation on which the nuclear program rests.

“Whether rightly or wrongly,” Ellsberg writes, “we are the only country in the world that believes it won a war ... specifically by bombing cities with weapons of mass destruction, firebombs, and atomic bombs — and believes that it was fully justified in doing so. It is a dangerous state of mind.”

Ellsberg’s analysis reaches back to the Manhattan Project of the 1940s, occasionally dwelling on episodes that have been exhaustively explored elsewhere. In his best chapters, he’s right there in the room, helping to craft America’s nuclear-weapons policy for Defense Secretary Robert McNamara and others.

In October 1961, as a consultant working with the Air Force, Ellsberg helped write a seemingly minor speech for Roswell Gilpatric, the deputy defense secretary in the Kennedy administration. Among the lines Ellsberg added was one suggesting that Soviet aggression in Europe might force the U.S. to use a nuclear weapon. Soviet leader Nikita Khrushchev didn’t take the threat lightly, and within a year, he put Soviet missiles in Cuba. Says Ellsberg: “I had done my part in greasing the skids toward the Cuban missile crisis.”

Around the same time, Ellsberg learned that President John F. Kennedy’s predecessor, Dwight Eisenhower, had empowered a small number of top-level military officers “to use nuclear weapons without immediate presidential authorization” in the event of a communications failure or the incapacitation of the president. Ellsberg believes that similar procedures have remained in place ever since — a sharp contrast to what the American public is often told.

“The theatrical device represented by the president’s moment-by-moment day-and-night access to the ‘football,’ with its supposedly unique authorization codes, has always been exactly that: theater — essentially a hoax,” he writes. “Whatever the public declarations to the contrary, there has to be delegation of authority and capability to launch retaliatory strikes, not only to officials outside the Oval Office but outside Washington too, or there would be no real basis for nuclear deterrence.”

Ellsberg, of course, worries about what might happen during Donald Trump’s presidency. He says there’s “ample evidence” that Trump is “mad.” But he draws a false equivalence when he stresses that Trump’s refusal to rule out the “nuclear first-use option” mirrors Hillary Clinton’s position — it’s a comparison that ignores the degree to which Clinton’s experience and understanding of history might have informed her decisions as commander in chief. It’s true, as Ellsberg says, that the “mortal predicament” of nuclear weapons is bigger than any single politician. But it’s also true that some presidential hopefuls are a lot less scary than others.

In the book’s final pages, Ellsberg makes several admittedly “quixotic” recommendations. These include the implementation of “a U.S. no-first-use policy” and the elimination of the “land-based leg of the nuclear ‘triad.’” Ellsberg isn’t optimistic that these things will happen — but he maintains that they must. “This is not a species to be trusted with nuclear weapons,” he says. “And that doesn’t just apply to ‘crazy’ third world leaders.”

Kevin Canfield has written for Bookforum, Film Comment and other publications. Email: books@sfchronicle.com